The primary objectives of the proposed research are: 1. To isolate and chemically characterize the hemolytic, leukocidal, and lethal factor or factors from Fusobacterium necrophorum K4 culture supernatants. 2. To determine if the hemolytic, leukocidal, and lethal factors in the F. necrophorum K4 culture supernatant are cell-associated. 3. To determine the specificity of the leukocidal factor for polymorphonuclear leukocytes and macrophages. 4. To characterize the immunogenic factor in the F. necrophorum K4 culture supernatant which is responsible for protecting mice against infection with F. necrophorum K4. The primary methods to be used are: 1. Chromatographic methods for isolating the hemolytic, leukocidal, and lethal factor(s) from the F. necrophorum K4 culture supernatant. 2. Enzyme-linked immunosorbent assay for determination of antibody titers in immunized animals and detection of the hemolytic, leukocidal, and lethal factor(s) in F. necrophorum cell fractions. 3. Limulus assay for determination of the lipopolysaccharide content of F. necrophorum cell preparations.